The present invention relates to replaceable friction elements for use in frictional connection of separable and removable dental prostheses, which prostheses consist of male and female parts.
In dental prostheses, special connecting elements are used for anchoring a removable prosthesis part on the denture remaining in the jaw. There are distinctions among these holding or connecting elements, resilient connecting elements, hinge-like connecting elements and rigid connecting elements. The present invention refers to resilient and rigid connecting elements, in which the holding function between the male and the female parts is produced by means of friction, and possibly also additionally by means of a detent connection.
To permit the desired removal of the prosthesis, for instance to clean it, without damaging the remaining denture, the friction between the male and female parts should not exceed a given amount. Detachment forces of between 300 and 500 grams are favorable. When the prosthesis is worn, the cooperating friction surfaces of the male and female parts become worn, their friction is lost, and the prosthesis becomes loose. There are a number of known solutions for remedying this, for instance, a so-called dovetail abutment with a replaceable metal bolt/spiral spring combination or a so-called snap lock with a metal ball/spiral spring combination. The spiral spring produces the pressure between the male and female parts which produces the holding force via the coefficients of friction of the parts. In addition, a detent recess can be worked into the surface opposite the ball or bolt so that the hold between the male and female parts is not only frictional but also by detents.
Another prefabricated friction element, which may also act as a detent, is known, for instance, from Federal Republic of Germany Publication A-33 35 904, which corresponds to European Patent Document No. 013667. That construction has an extremely short structural height because it uses a flat spring which is bent into an S-shape.
For use between telescopable parts, a so called TK snap is available. This is a prefabricated functional element with a resilient spherical friction surface. The spherical surface and spring are formed of a single sheet metal part which is shaped in a suitable manner and which is inserted into an undercut depression of suitable size.
One big problem in dental prosthesis is the small amount of space available for the connecting elements. All known connecting elements which have springs, regardless of whether they are spiral springs, flat springs or spring plates, require a substantial structural volume. Otherwise, the springs, which, as mentioned, produce frictional forces of 300 to 500 grams, become fatigued or break within a short period of time.
Another problem in connection with these connecting elements is oral hygiene. Saliva and traces of food enter the cavities which receive the springs, bolts and/or balls. The contaminants cannot be removed upon the normal cleaning of the prosthesis because when the prosthesis has been removed, the opening is closed by the ball pin and/or spring element which produces the friction or detent.